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The spike protein of SARS-CoV-2 binds to the ACE2 receptor via its receptor-binding domain (RBD), with the RBD–ACE2 complex presenting an essential molecular target for vaccine development to stall the virus infection proliferation. The computational analyses at molecular, amino acid (AA), and atomic levels have been performed systematically to identify the key interacting AAs in the formation of the RBD–ACE2 complex for SARS-CoV and SARS-CoV-2 with its Alpha and Beta variants. Our study uses the molecular dynamics (MD) simulations with the molecular mechanics generalized Born surface area (MM-GBSA) method to predict the binding free energy (BFE) and to determine the actual interacting AAs, as well as two ab initio quantum chemical protocols based on the density functional theory (DFT) implementation. Based on MD results, Q 493 , Y 505 , Q 498 , N 501 , T 500 , N 487 , Y 449 , F 486 , K 417 , Y 489 , F 456 , Y 495 , and L 455 have been identified as hotspots in SARS-CoV-2 RBD, while those in ACE2 are K 353 , K 31 , D 30 , D 355 , H 34 , D 38 , Q 24 , T 27 , Y 83 , Y 41 , and E 35 . RBD with Alpha and Beta variants has slightly different interacting AAs due to N501Y mutation. Both the electrostatic and hydrophobic interactions are the main driving force to form the AA–AA binding pairs. We confirm that Q 493 , Q 498 , N 501 , F 486 , K 417 , and F 456 in RBD are the key residues responsible for the tight binding of SARS-CoV-2 with ACE2 compared to SARS-CoV. RBD with the Alpha variant binds with ACE2 stronger than the wild-type RBD or Beta. In the Beta variant, K417N reduces the binding, E484K slightly enhances it, and N501Y significantly increases it as in Alpha. The DFT results reveal that N 487 , Q 493 , Y 449 , T 500 , G 496 , G 446 , and G 502 in RBD of SARS2 form pairs via specific hydrogen bonding with Q 24 , H 34 , E 35 , D 38 , Y 41 , Q 42 , and K 353 in ACE2.

An effective computational scheme to calculate the complete set of independent elastic constants as well as other structural parameters including bulk modulus, shear modulus, Young's modulus, and Poisson's ratio for crystals is reported. The scheme is based on the stress–strain analysis approach with the appropriate selection of strain governed by symmetry consideration. The first principles Vienna ab initio simulation package (VASP) is used in stress calculations. Comprehensive tests were performed for α‐SiO2 and spinel MgAl2O4 with different exchange‐correlation potentials, and different sets of computational parameters to investigate the relative accuracies of the calculations. A wide range of oxides, nitrides, and carbonate crystals with different crystal symmetries were chosen to test the scheme under both LDA and GGA approximations at zero temperature and pressure. Some of these calculations for large complex crystals are believed to be attempted for the first time. The calculated elastic constants show quite good agreement with the existing experimental data for almost all the examined systems with the exception of the relatively soft material such as α‐SiO2 and the C14 parameter of some trigonal crystals expressed in the hexagonal form such as in α‐Al2O3. Other structural properties derived from the elastic constants also show good agreements with the measured values.